1. Field of the Invention
The present invention relates to a mechanical ignition sensor which senses a state of a sudden deceleration of a vehicle so as to actuate an ignitor member.
2. Description of the Related Art
For example, an air bag device equipped on a vehicle is provided with a gas generator having a mechanical ignition sensor. When a vehicle is brought into a state of a sudden deceleration, this state is sensed by the mechanical ignition sensor and the gas generator operates and instantaneously generates gas so as to inflate an air bag body within the air bag device.
As shown in FIG. 8, a mechanical ignition sensor 100 used in the air bag device as described above is basically formed from an ignition pin 104 for igniting an ignitor 102, an inertial mass body 106 inertially moving by a rapid deceleration, and a trigger lever 108 interposed between the ignition pin 104 and the inertial mass body 106 so as to prevent movement of the ignition pin 104.
The trigger lever 108 is usually in a state in which an engaging portion 108A engages with the inertial mass body 106. When the inertial mass body 106 moves in an upper direction in FIG. 8 (i.e., the direction indicated by arrow F in FIG. 8), the engaging portion 108A enters a slit 110 formed in the inertial mass body 106 and rotates around a shaft 112 in a counterclockwise direction in FIG. 8 (i.e., the direction indicated by arrow R in FIG. 8). As a result, the engaging portion 108A of the trigger lever 108 is released from a state of engaging with the ignition pin 104.
Further, the inertial mass body 106 is urged by a spring 114 in a direction opposite to the direction of arrow F in FIG. 8. When deceleration greater than the urging force of the spring 114 acts on the sensor 100, the inertial mass body 106 starts moving in tile direction indicated by arrow F in FIG. 8.
However, in the above-described mechanical ignition sensor 100, immediately after the engaging portion 108A of the trigger lever 108 starts entering the slit 110 formed in the inertial mass body 106 at the same time when the inertial mass body 106 moves, if a sliding resistance between the engaging portion 108A and the slit 110 increases, a rotational resistance of the trigger lever 108 may increase.